Pneumatic Boat Lift with Boat-Carrying and Boat-Guiding Air Tanks

ABSTRACT

A pontoon boat lift features tanks adjacent opposite sides thereof with upper walls slopes upwardly in a laterally outward direction. In lowered positions of the tanks, top ends of the sloped walls remain above water for visual and physical guidance of the pontoon boat into a position placing pontoons thereof between the outwardly sloped walls and over submerged portions of the lowered tanks, thereby allowing subsequent seating of the pontoons on said sloped walls during raising of the air tanks to lift the pontoons from the water. Buoyancy control for raising and lowering of the tank is effected by controlling air and water content thereof. The tanks are arranged to trap sufficient air therein to keep the lift buoyant to prevent sinking without using legs to support the boat lift on the sea, lake or river bed. The lift is adjustable in width and length for boats of varying size.

FIELD OF THE INVENTION

The present invention relates to a lift for raising a pontoon boat out of a body of water, and more particularly to such a lift that employs floating air tanks on which the boat is directly supported when the lift is raised.

BACKGROUND OF THE INVENTION

In the field of watercraft, it is sometimes desirable to store a watercraft in an elevated position over a body of water, for example to avoid the hassle of repeatedly launching a boat into the body from shore while also avoiding complications that can arise from keeping the boat in the water when out of use. Accordingly, several boat lift designs have been previously proposed.

Many prior art boat lifts are mechanical in design, for example employing a bulky structure having a base frame that carries a movable section for lifting the boat, for example through operation of a winch. Other boat lifts employ buoyancy based designs, where the lifting action is instead provided by pontoons or inflatable members whose floatation is used to elevate the boat out of the water.

Examples of boat lifts and dry docks of such floating design are disclosed in U.S. Pat. Nos. 5,860,379, 6,526,902, 7,069,872, 7,117,809, 7,213,531, and 7,426,898, U.S. Patent Application Publication Number 2005/0217552, and U.S. Design Pat. No. D619325.

However, the forgoing floating lift designs have been developed for monohull (single-hulled) watercraft, and accordingly are not configured for lifting pontoon boats, which feature a platform spanning a distance between two pontoons adjacent opposite sides of the boat. Applicant has developed unique pneumatically operated boat lifts where the variable-buoyancy air tanks not only control raising and lowering of the lift through introduction and evacuation of air thereto and therefrom, but also act as the actual support members on which the raised boat is seated during lifting and storage, provide guide surfaces to direct the boat into the correct position for lifting, and can be configured in number and shape for compatibility with monohull watercraft and pontoon boats or other multihull watercraft.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a boat lift for elevating a boat out of a body of water, the boat lift comprising:

a frame having front and rear ends spaced along a longitudinal dimension and opposite first and second sides spaced apart in a transverse dimension perpendicular to the longitudinal dimension;

a plurality of tanks mounted to the frame, each tank comprising a shell having a hollow interior, an air flow port that opens through the shell into the hollow interior, a water port opening through the shell into the hollow interior adjacent a bottom of said hollow interior, and at least one outwardly sloped wall at an upper end of the shell that slopes upwardly above the frame along the transverse dimension thereof toward a respective side of the frame;

an air pumping mechanism connected to the air flow port of each tank and operable to convey air into the hollow interior thereof to float the tanks into raised positions situating upper ends of the outwardly sloped walls above water level; and

an air release mechanism connected to each tank and operable to release air from within the hollow interior thereof to decrease the buoyancy of the tanks for movement from the raised positions to lower positions, in which lower ends of the outwardly sloped walls and portions of the outwardly sloped walls that are found above water level in the raised positions are submerged below water level while the upper ends of the outwardly sloped walls remain above water level.

Preferably the plurality of tanks comprise at least one first-side tank mounted to the frame adjacent the first side thereof and at least one second-side tank mounted to the frame adjacent the second side thereof, the outwardly sloped wall of each first-side tank sloping upwardly away from the second side of the frame the outwardly sloped wall of each second-side tank sloping upwardly away from the first side of the frame.

In one embodiment, suitable for use with a pontoon boat, the at least one first-side tank comprises front and rear first-side tanks respectively disposed adjacent the front and rear ends of the frame, and the at least one second-side tank comprises front and rear second-side tanks respectively disposed adjacent the front and rear ends of the frame.

In such an embodiment, preferably the shell of each first-side tank and each second-side tank further comprises an inwardly sloped wall sloping upwardly along the transverse dimension of the frame in a direction away from the outwardly sloped wall of said tank and toward the side of the frame opposite said tank to give a concave shape to the upper end of the shell.

In another embodiment, suitable for monohull watercraft, the plurality of tanks comprise:

a first-side rear tank mounted to the frame adjacent a rear end of the frame and adjacent the first side of the frame;

a second-side rear tank mounted to the frame adjacent the rear end of the frame and adjacent the second side of the frame; and

a front tank mounted to the frame adjacent a front end thereof and positioned centrally between the rear tanks in the transverse direction of the frame;

and wherein the outwardly sloped walls of the first-side and second-side rear tanks slope upwardly away from the second and first sides of the frame respectively, and the front tank comprises two of said outwardly sloped wall, each of which slopes upwardly away from the other along the transverse dimension of the frame in a toward a respective on of the first and second sides of the frame to give a concave shape to the upper end of the shell of said front tank.

Preferably the hollow interior of the shell of each tank features a divider that divides an upper region of the hollow interior of the tank into separate portions on opposite sides of said divider, and the air release mechanism is operable to release air from each tank from a location above a lowermost point of the divider on only one side thereof.

Preferably the divider comprises a channel recessed into the upper end of the shell.

Preferably the air release mechanism comprises one or more valves each installed an air passage that communicates with the hollow interiors of one or more of the tanks, each valve being operable to selectively open said air passage to release air from the hollow interior of the one or more tanks, and close said air passage, to retain air within the hollow interior of the one or more tanks.

Preferably the air passage in which each valve is installed connects the air pump to the one or more tanks, and the air pump is operable to convey air to said one or more tanks when said valve and said passage are open.

Preferably the one or more valves comprises a plurality of valves, each operable to control air flow with the hollow interior of a respective one of the tanks.

Preferably there are provided valve controls that are connected to the plurality of valves and operable for control thereof independently from one another.

Preferably there are provided pump controls that are connected to the air pumping mechanism and operable for control over air-filling of each tank with tank independently from one another.

The frame may comprise a width adjustment mechanism operable to change a width of the frame between the opposite sides thereof.

The frame may comprise a length adjustment mechanism operable to change a length of the frame between the front and rear ends thereof.

Preferably each adjustment mechanism comprises at least one set of telescopically mated frame members, said frame members being slidable into, and lockable together in, different relative axial positions with one another to change an effective axial length spanned by said set.

Preferably there is provided a stop device projecting upward to an elevation above the upper ends of the tanks adjacent the front end of the frame to limit movement of the boat over the frame from the rear end when the tanks are in the lowered positions.

Preferably the stop device comprises at least one resilient bumper presenting an impact surface facing toward the rear end of the frame for contact therewith by the boat.

According to a second aspect of the invention there is provided a method of raising a boat from a body of water, the method comprising:

with at least one front air tank and at least two rear air tanks of a boat lift partially submerged to position a lower end of an upwardly and laterally outwardly sloped wall of each tank below water level and position an upper end of said sloped wall above water level, maneuvering the boat toward a rear end of a boat lift where said rear tanks are positioned adjacent opposite sides of said boat lift;

moving a front end of the boat over the rear end of the boat lift to position the boat over submerged portions of the rear tanks;

continuing to move the boat toward a front end of the boat lift along a longitudinal dimension thereof to also position the boat over a submerged portion of each front tank;

introducing air into the front and rear tanks to increase the buoyancy thereof and raise the tanks of the lift upward against the boat until the buoyancy of the tanks is sufficient to also raise the boat, now seated atop the tanks, to a raised position fully withdrawn from the body of water.

The step of continuing to move the boat toward the front end of the boat lift may comprise using the outwardly sloped surfaces of the tanks of the boat lift to guide the boat along the longitudinal dimension of the boat lift.

According to a third aspect of the invention there is provided a method of lowering a boat into a body of water, the method comprising, with the boat seated above water level atop buoyant tanks of the boat lift adjacent opposite sides thereof, releasing air from hollow interiors of the tanks and taking on water in said hollow interiors of said tanks to decrease the buoyancy thereof and lower the tanks until the tanks are sufficiently submerged below water level to float the boat in the body of water independently of the tanks of the boat lift.

Lowering of the tanks may comprise lowering the tanks only to a position where upper ends of upwardly and laterally outwardly sloped walls at upper ends of the tanks remain above water level, and wherein the method further comprises withdrawing the boat from over the boat lift by maneuvering the boat along a longitudinal direction of the boat lift with guidance from the outwardly sloped walls of the tanks of the boat lift.

Preferably the step of releasing air from the hollow interiors of the tanks comprises attaining a minimum achievable air level in the hollow interiors of said tanks, at which the tanks still contain a level of air that is sufficient to make the boat lift buoyant alone, but not with the boat seated thereon.

According to a fourth aspect of the invention there is provided a boat lift for elevating a boat out of a body of water, the boat lift comprising:

a frame;

a plurality of tanks mounted to the frame, each tank comprising a shell having a hollow interior, an air flow port that opens through the shell into the hollow interior, and a water port opening through the shell;

an air pumping mechanism connected to the air flow port of each tank and operable to convey air into the hollow interior thereof to float the tanks into raised positions; and

an air release mechanism connected to each tank and operable to release air from within the hollow interior thereof to decrease the buoyancy of the tanks for movement from the raised positions to lower positions;

wherein the hollow interior of the shell of each tank features a divider that divides an upper region of the hollow interior of the tank into separate portions on opposite sides of said divider, and the air release mechanism is operable to release air from each tank from a location above a bottom of the divider on only one side thereof to thereby trap air on the on the side of the divider when a water level in the hollow interior of the tank reaches the divider.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate exemplary embodiments of the present invention:

FIG. 1 is a perspective view of a pontoon boat lift according to a first embodiment of the present invention.

FIG. 2 is a schematic end view of the pontoon boat lift in a lowered position in a body of water.

FIG. 3 is a side view of the pontoon boat lift in a raised position elevating a pontoon boat out of the body of water.

FIG. 4 is a perspective view of an air tank of the pontoon boat lift.

FIG. 5A is an end view of the air tank of FIG. 4.

FIG. 5B is a bottom plan view of the air tank of FIG. 4.

FIG. 6 is a schematic illustration of a control system for controlling the variable buoyancy of the pontoon boat lift.

FIG. 7 is a schematic illustration of a frame-adjustment mechanism of the pontoon boat lift.

FIG. 8 is a schematic plan view of a monohull boat lift according to a second embodiment of the present invention.

FIG. 9 is a schematic front end view of the monohull boat lift.

DETAILED DESCRIPTION

FIG. 1 shows a pontoon boat lift 10 of the present invention configured for selective raising and lowering of a pontoon boat out of and back into a lake, river, sea or other body of water. The boat lift 10 features a frame 12 defining a rectangular shape of the boat lift 10 in plan view, and four air tanks 14 each mounted to the frame 12 at a respective one of the four corners of its rectangular shape. Each tank 14 is a polyhedron in overall shape, featuring a concave upper end 16 having two sloped rectangular walls 18, 20 that join one another at their lower edges to define a V-shaped channel 22 between them. An outer one of the sloped wall angles upwardly and laterally outwardly toward the respective side of the frame, while the inner one angles upwardly and laterally inward toward the transverse center of the frame. A control housing 24 carried at a distance above the frame by an upright 25 mounted thereon contains an air pump therein, the output of which feeds the inlet of a four-outlet manifold whose four outlets are respectively connected to the four air tanks 14 by four air hoses 26. Four valves are installed between the outlet of the air pump and the four air hoses 26 in order to allow selective opening and closing of the airflow passages extending between the air pump and the air tanks through the hoses. Through control of the air pump and the valves, an operator can control to level of air in the four tanks in order to control the buoyancy thereof for adjustment between a maximum buoyancy, which lifts a substantial majority of the tank out of the water and provides enough buoyancy to support the lift and the boat to be carried thereby, and a minimum buoyancy, in which the peaks 28 of the upper ends 16 of the tanks 14 remain above water level while the lower point of the V-shaped channel 22, and the remainder of the tank therebelow, is submerged below the water level.

To lift a pontoon boat 100, the tanks of the lift are reduced to their minimum buoyancy so as to be substantially submerged, and the boat is driven into a position overlying the substantially submerged boat lift, particularly with the pontoons 102 of the boat each lying over the concave upper ends of the two air tanks at a respective side of the boat lift frame so that a lower portion of the pontoon's cross section resides between the two peaks 28 of the tank's concave upper end. With the boat so positioned, the air pump of the boat lift is activated in order to feed air through the air hoses 26 and into hollow interiors of the air tanks via airflow ports 27 passing through end walls of the tanks. The filling of air into the tanks displaces water out of the tanks through holes in bottom walls thereof located opposite the concave upper ends of the tanks.

A maximum buoyancy of each tank corresponds to an entirely air-filled state of its hollow interior, achieved by successful displacement of all water from the tank by the pumping of air thereinto. The dimensions of tanks are selected so that the volume of air contained in the four tanks when filled to this maximum level provides a sufficient buoyant force to overcome the weight of the entire boat lift and the pontoon boat to be lifted thereby. Accordingly, the filled air tanks rise from their lowered positions as their buoyancy increases with the added air, forcing the sloped walls of the concave upper end of the tanks upward against the undersides of the pontoons of the boat, so that as the buoyancy force increases to a level sufficient to overcome the combined weight of the boat lift and the boat, the tanks continue to rise towards their fully raised positions, carrying the pontoon boat upward with them. When fully raised, the tanks are positioned at a level placing the lower points of their concave upper ends above water level, and thus likewise positioning the lowermost extent of each pontoon of the boat above water level.

When it is desirable to lower the boat back into the water, the control system is used to open the valves between the air pump and the air tanks so air from the air tanks can flow back through the air hoses, manifold and pump back into the atmosphere. That is, the interior of each tank is put into fluid communication with the atmosphere through the air hose, manifold and pump, and under the weight of the boat and the weight boat lift acting downward on the air tanks, the tanks will sink downward, and water entering the tanks during this sinking action displaces the air from the interior of each tank through the connected air hose. However, the airflow port of each tank is positioned on an end wall thereof at an elevation adjacent the upper end of the tank at a distance above the lowest point of the upper end's V-shaped concavity. This way, when the tank sinks to a partially submerged position where the water level reaches the lowest point of the V-shaped channel, the air inside the tank on the side of the V-shape channel opposite the airflow port becomes trapped within the tank, as it is blocked from crossing the tank to the airflow port by the sloped upper wall defining that side of the V-shaped channel and the surface of the water that has reached the elevation of that sloped wall's lower edge. As a result, each air tank always contains at least some air within its hollow interior. The tank dimensions are selected so that the air that becomes trapped in the peaked areas of the tank interiors on the sides of the V-shaped channels opposite the airflow ports of the tanks is sufficient to make the boat lift buoyant, but insufficient to also overcome the weight of the boat. As a result, with the tanks drained of air to this minimum-buoyancy level provided by the remaining trapped air, the weight of the boat on the tanks acts to submerges the tanks to a level where the boat instead becomes supported by the buoyancy effect between the water and the pontoons of the boat. At this point, with the boat itself now directly afloat on the water, the boat is driven out of the position overlying the boat lift, at which point the trapped air in the tanks of the boat lift will float the boat lift back up to its default position where the upper peaks of the tanks are elevated from the water, while the lower point of the V-shaped channel between the peaks is submerged. The boat lift is thus in a suitable position for return of the boat back over the lift to be raised again when ready for storage.

FIGS. 4 and 5 show a preferred shape of the air tanks of the pontoon boat lift, which are preferably identical in size and shape to one another for improved ease and cost of manufacture. The recessed or concave upper end 16 of the tank features the two sloped planar walls 18, 20 that converge downwardly toward one another and extend fully from one end of the tank to the other to define the V-shaped channel 22 running the full length of the tank. In the preferred embodiment, the sloped walls 18, 20 do not directly meet one another at their lower edges, but rather are integrally joined with one another at these edges by a U-shaped span 30 that dips downward between the lower edges of the sloped walls to define the lowermost point of the V-shaped channel. The dip provided at the bottom of the V-shaped channel by this U-shaped span 30 can accommodate the keel of a pontoon when peripheral surfaces of the pontoon curving upward and outward from opposite sides of the keel are seated on the sloped walls 18, 20 of the tank.

A peripheral groove 32 runs fully around the tank 14, and has a rectangular cross-section that recesses into otherwise-planar end walls 34, 36 and otherwise-planar side walls 38, 40 of the tank that project perpendicularly upward from respective sides of a rectangular bottom wall 42 of the tank. The peaked portions 28 of the tank on opposite sides of the V-shaped channel 42 are capped off by narrow top walls 44, 46 that lie parallel to the bottom wall 42 of the tank to obliquely join the upper ends of the respective sloped walls 18, 20 to the upper ends of the respective side walls 38, 40 of the tank. The bottom wall 42 features one or more openings through which water enters the hollow interior of the tank. For example, a single hole 42 a positioned centrally in the bottom wall, as shown in FIG. 5B, has been found to function suitably in prototypes of the pontoon boat lift, though it is expected the multiple holes at spaced positions over the area of the bottom wall would also provide suitable results.

The airflow port 27 of the illustrated tank is made in one of the end walls 36 of the tank, as shown in FIG. 5, beneath one of the narrow top walls 26 of the tank at a height above the low point of the V-shaped channel 22 at the bottom of the narrow U-shaped span 30 joining together the sloped walls 18, 20. This way, when water fills the interior of the tank to the level of the U-shaped span 30 at the bottom of the V-shaped channel 22, air found in the peaked portion of the tank on the opposite side of the V-shaped channel cannot reach the airflow port 27, thereby ensuring that some air remains trapped in the tank to retain a positive buoyancy of the boat lift and prevent the same from sinking to the lake, river or sea bed. In the illustrated embodiment, the airflow port of each tank is located near the inner side of each tank, leaving the trapped air in the outer half of the tank interior.

Turning back to FIG. 1, the peripheral rectangular groove 32 in each of the tanks is used to accommodate a full or partial cross-sectional area of rectangular tubing used to construct the illustrated frame 12 of the boat lift 10. The illustrated frame features side sections 48, 50 defining a longitudinal direction of the frame, and parallel end sections 52, 54 extending in a cross-wise or transverse direction of the frame to perpendicularly interconnect the two end side sections 48, 50 at opposite ends thereof. Two intermediate sections 56, 58 also perpendicularly interconnect the side sections 48, 50 in the cross-wise direction, but at intermediate positions along said side sections 48, 50.

The four air tanks 14 reside at inside the four corners of the rectangular layout of the end and side sections of the frame 12. Each frame section is a telescopic assembly, featuring two outer pieces of rectangular tubing of a first cross-sectional size, and a single inner piece of rectangular tubing of a second smaller cross-sectional size.

At each outer corner of the frame, i.e. each corner of the rectangular shape bound by the side and end sections of the frame, one outer piece of the respective end section 52, 54 is fixed to one outer piece of the respective side section 48, 50, for example by welding. This outer piece of the respective end section 52, 54 extends along the end wall of the respective tank 14 in the peripheral groove 32 thereof from this corner of the frame, and continues past the other end of the tank's end wall to a position lying between that tank and the other tank at the same end of the frame. Likewise, the outer piece of the respective side section 48, 50 extends along the side wall of the respective tank 14 in the peripheral groove 32 thereof from this corner of the frame, and continues past the other end of the tank's side wall to a position lying between that tank and the other tank at the same side of the frame.

At each inner corner of the frame, i.e. at each connection of each intermediate section 56, 58 to each of the side sections 48, 50, one of the two outer pieces of the intermediate section 56, 58 is fixed to one of the two outer pieces of the respective side section 48, 50 where that outer piece of the side section exits the peripheral groove 32 of the respective tank 14 at the outer side wall thereof. The outer piece of the intermediate section extends from the respective outer piece of the respective side section along the respective end wall of the respective tank in the peripheral groove 32 thereof from this inner corner of the frame, and continues past the other end of the tank's end wall to a position lying between that tank and the other tank at the same end of the frame

With reference to FIG. 7, the inner tubular piece 60 of each section has its opposite ends nested within the hollow interior of the two outer tubular pieces 62, 64 of the same section, whereby each section can be telescopically expanded by sliding the free ends 62 a, 64 a of the two outer pieces 62, 64 away from one another along the inner piece 60, or telescopically collapsed by sliding the free ends of the two outer pieces toward one another along the inner piece. Such telescopic adjustment of the side sections of the frame allows the length of the overall boat lift to be changed, while such telescopic adjustment of the end and intermediate sections of the frame allows the width of the overall boat lift to be changed. A minimum attainable length or fully collapsed state of any section thus corresponds to abutment of the free ends 62 a, 64 a of the outer pieces 62, 64 against one another. A maximum attainable length or fully expanded state of any section corresponds to a state in which the opposite ends of the inner piece 60 extend only a slight distance into each of the outer pieces, just far enough to achieve a coupling of the inner piece to each outer piece. Although omitted in the drawings for ease of illustration, it will be appreciated that the air hoses connected to the tanks should be of sufficient length to provide slack when the frame of adjustable-frame embodiments is in a collapsed minimum-size configuration, and still reach the tanks when the adjustable frame is expanded into an enlarged state.

Releasable locked coupling of the inner member to the outer members to lock a selected effective length of the section between its opposite ends defined at the respective corners of the frame may achieved through use of locking pins that are passed through alignable through-holes in the outer and inner tubular pieces. For example, the inner piece may feature a series of horizontal or vertical through-holes 66 spaced apart therealong and each outer piece having at least one through hole 68 of the same orientation located near the free end 62 a, 64 a of the outer piece between the two respective tanks. Alignment of the holes 68 in the outer pieces 62, 64 with select ones of the holes 66 in the inner piece 60 can thus achieve a selected section length, which is then locked by passage of a respective locking pin through each of the two aligned pairs of holes, for example using ball detent pins 69 or other known locking pin configurations.

The tanks are preferably made of plastic material, for example using rotational moulding, blow moulding or injection molding techniques. For the two tanks on each side of the frame, the concave recesses or channels at the upper ends of the tanks are aligned with one another to share a common linear axis running along the bottom of the two V-shaped channels. To prepare the boat for lifting, it is driven forwardly toward the lift with its two pontoons each generally aligned with the axis of the two tanks on a respective side of the boat lift frame. As the leading ends or tips of the pontoon reach an access end or rear end 12 a of the boat lift frame and accordingly ride into the V-shaped channels of two tanks at this end of the frame, as accommodated by the partially submerged condition of these channels when the lift has been prepared for use by putting the air tanks in their minimum buoyancy condition, the two sloped walls of each of these tanks act as guide surfaces contacting the curved peripheral portions of the underside of the pontoon on opposite sides of a keel or central axis of the pontoon. The downward sloping together of these guide walls of the tank encourages alignment of the keel or lowermost point of the pontoon's cross section directly over the bottom of the V-shaped channel formed between these sloped tank walls, thus guiding the each pontoon of the boat into alignment with the shared tank axis of the two tanks on the respective side of the lift, so that continued forward movement of the boat toward the front end 12 b of the boat lift frame 12 opposite the access end 12 a at which the boat first reached the lift will move leading portions of the two pontoons over into positions aligned over the V-shaped channels of the two tanks at the front end 12 b of the boat lift.

A stop assembly 70 mounted at the front end 12 b of the boat lift frame 12 features two support arms 72 projecting obliquely upward and forward from the front end frame section 54 to carry a pair of bumpers 74 at a height above the tanks 14 at a common distance past the front end of the frame so that when the boat has reached a ready-to-lift position in which its two pontoons overlie all four tanks of the lift, contact of the front end of the boat with the bumpers will prevent the boat from over-shooting the lift, or in other words prevent the boat from continuing forward so far as to bring the rear ends of the pontoons past the forward ends of the tanks at the rear access end 12 a of the boat lift. The bumpers are preferably each resiliently padded to provide a resilient impact surface 74 a facing the rear access end of the boat lift to minimize the potential for damage of the boat through impact with the bumpers. The number of bumpers may be increased or decreased from the two bumpers of the illustrated embodiment.

FIG. 6 schematically illustrates the control system 80 for the above described boat lift. The pump 82 feeds each of the air hoses 26 through via a manifold 84, each outlet of which is openable and closeable by a respective valve 86. A suitable manifold may be constructed from conventional pipe components, for example using commercially available T-connectors and elbow joints. In the illustrated embodiment, the air pump is controlled by a simple on-off button or switch, and the valves 86 are each of a manual controlled variety each having a respective actuator for opening and closing the valve. It will be appreciated that electronically controlled valves may alternatively be employed. To raise the boat lift, each of the valves 86 are opened and the pump activated to convey air into each of the four tanks through the respective air hoses. The individual and independent control of the valves gives the operator independent control over the buoyancy of each tank to allow the operator to compensate for the unique weight distribution of the boat in question to achieve a level orientation of the boat when carried on the tanks. The operator can also monitor the water around each tank to watch for air bubbles rising to the surface around the tank, providing visual indication that the tank interior has reached its full air capacity. At this point, the respective valve at the control housing can be closed, so that output from the pump is not being wasted on an already-filled tank, and can instead be directed through the remaining open valves to fill the other tanks. When all tanks have been sufficiently filled to provide the sufficient buoyancy to the respective corner of the lift to fully raise the respective corner of the boat, whether realized through recognition of sufficient lifting of the boat at each tank or by recognition of a completely air-filled tank by bubbling in the water therearound, and all the valves are thus closed, the air pump is deactivated, either manually or by tripping of a safety cutoff switch when a predetermined pressure limit has been reached. With the valves closed to prevent airflow from the tanks back through the air hoses, manifold and pump, the air level in each tank is retained, thereby maintaining the lift in its raised elevating the lift-carried boat out of the water.

The boat lift above provides several features not found in the prior art referenced in the background section herein above, including a unique layout of air tanks at opposing sides of a frame with concave upper sides for guiding pontoons of a pontoon boat into a suitable position for direct lifting thereof by the air tanks themselves, a unique arrangement for only partially draining the tanks of air when taking on water in the same to lower the boat lift so that the boat lift always remains buoyant and only partially submerges its tanks when preparing to accommodate the pontoon boat over the lift without relying on supports legs the sit on the lake/river/sea bed when the lift is lowered, and a unique arrangement for adjusting both the length and width of the frame for maximum adaptability of the same frame for compatibility with pontoon boats of varying size.

It will be appreciated that one or more of these advantageous features and functions may be included independently of the presence or absence of others in different embodiments of the present invention, and that modifications to the illustrated particulars of these features may be made without detriment to the beneficial functionality thereof.

FIGS. 8 and 9 schematically illustrate a second embodiment boat lift 10′ intended for use with a monohull watercraft, as generally shown using broken lines. The boat lift again includes a frame 12′ of tubular metal construction and a plurality of air tanks controlled in the same manner as described above for the pontoon boat lift 10 of the first embodiment. The second embodiment lift 10′ differs primarily in that a single front tank 14 replaces the two front tanks of the first embodiment, and the two rear tanks 14′ do not have the symmetric V-shaped top end concavity of the front end tank, which has the same tank configuration as first embodiment where two sloped walls angle upwardly and laterally outward away from a lowest point at the widthwise center of the tank toward opposite sides thereof.

Instead, the upper end of each rear tank 14′ has a main rectangular wall 90 sloping upwardly and laterally outward from the top end of an inner one 92 of its two parallel side walls running in the longitudinal direction of the frame. This sloped main wall 90 spans more than half of the tank's width, extending from the inner side wall 92 toward the narrow top wall 44 that juts a short distance horizontally inward from the top end of the opposing outer side wall 94. A small V-shaped channel 96 significantly narrower and steeper than the V-shaped channel of the front tank 14 runs in the longitudinal direction of the frame separates the upper end of the sloped main wall 90 from the narrow top wall 44 at a position laterally outward from the widthwise center of the tank. In the illustrated embodiment, one of the two sloped sides or walls of the small V-shaped channel, specifically the side of the channel that meets the narrow top wall 44, is taller than the other so that the corner between the narrow top wall 44 and this taller side of the V-shaped channel 96 lies in the plane of the main sloped wall 90.

The narrower channel 96 of the rear tank is not intended to receive a portion of the boat like the larger channel 22 of the front tank 14, but does cooperate with the airflow port 27′ of the tank in the same manner as the first embodiment to trap a volume of air in the tank to retain a degree of buoyancy and prevent sinking of the lift to the sea/river/lake bottom. That is, the airflow port 27′ of each rear tank 14′ is situated above the lowermost point of the V-shaped channel 96 on one side thereof, particularly the inner side thereof nearer the widthwise center of the boat lift in the illustrated embodiment. Being the only airflow port of the illustrated tank, it defines the only passage for airflow into and out of the tank when the bottom portion of the tank is filled with water. Accordingly, when the tank takes on a level of water reaching the lowermost point of the V-shaped channel 96, remaining air above the surface of the water on the side of the V-shaped channel opposite the airflow port 27′ becomes trapped as the side of the channel and the surface of the water block the air from reaching the airflow port located across the channel. The dimensions of the tank are selected so that this volume of air trapped in each of the rear tanks, and the volume air similarly trapped in the front tank, are sufficient to make the overall boat lift buoyant.

It will be appreciated that the small channel running the length of the tank interior to provide this air-trapping action need not be V-shaped, and for example may have two vertical side instead of two sloped side walls that intersect or are joined together by a bottom wall at their lower ends. In another embodiment, the division of the upper region of the tank's interior into separate portions on opposite of a divider for the purpose of trapping air on one side thereof may be achieved by through use of a dividing structure other than a channel recessed into the upper end of the tank, for example by a divider plate fixed to the interior of a tank that is formed through the assembly of multiple pieces joined together in a fluid tight manner.

Operation of the second embodiment lift is similar to the first embodiment. To prepare for receipt of the boat, the valves of the lift's control system are opened, if not already in such a condition, to ensure that the tanks have taken on sufficient water to partially submerge the tanks to a level placing the lower ends of the sloped walls 18, 20, 90 of the front and rear tanks 14 a, 14 b beneath the surface of the water. The front end of the boat is aimed toward the transverse center of the boat lift as the boat approaches the rear end thereof so as to direct the boat toward the front air tank 14 positioned centrally between the rear tanks 14′ along the frame's transverse dimension. The boat is maneuvered toward the front end of the boat lift, with the downwardly-converging/upwardly-diverging sloped walls 90 of the two rear tanks 14′ guiding the front end of the boat into the V-shaped channel between the sloped walls 18, 20 of the front tank 14 as the wider portion of the boat's hull reaches and slides against these sloped walls 90 of the rear tanks 14′. When the boat stops, the submerged portion of the front tank's V-shaped channel underlies a narrow front portion of the boat's hull, and the submerged inner sides of the rear tanks underlie more rearward portions of the hull on either side of its transverse center, for example on opposite sides of a keel of the hull. The pump of the boat lift control system is activated to pump air into the tanks, thereby increasing the buoyancy thereof, until the tanks are sufficiently elevated to carry the boat fully out of the water.

The frame 12′ of the second embodiment may be adjustable in size like the first embodiment. Where the same general telescopic assembly described for the first embodiment is used, one notable difference for embodiments where the frame sections are also recessed into the periphery of the air tanks is that the pin holes for locking the outer pieces of each telescopic frame section to the inner piece thereof should include pin holes in the outer pieces of the width-wise telescopic sections 54′, 58′ at the front air tank 14 a that are positioned far enough from the free ends of the outer pieces to reside laterally outward from the front air tank when the frame is fully collapsed widthwise. This is shown in FIG. 8 where the locking pins 69 on these two sections 54′, 58′ are situated laterally outward from the front tank.

Although the first pontoon-boat embodiment employs two sloped walls at the top end of each tank to form a V-shaped channel for guiding the pontoons of the boat and preventing the same from moving laterally outward from over the tanks, two pontoon-abutting walls sloping in opposite directions on each tank may not be necessary. The upward and laterally outward slope of the outer walls of the tanks would alone prevent lateral displacement of either pontoon of the boat from over the lift and encourage alignment of the pontoons in the longitudinal direction of the lift. For example, the four tanks of the pontoon boat embodiment may be replaced with the rear-tank style of the second embodiment, where the upper end of the tank is primarily sloped in a single direction. However, the concave upper end of the first embodiment tanks is still preferred for pontoon boat lifts, for example to prevent sliding of either pontoon downwardly and inwardly off the respective tanks in a manner tipping the boat about its longitudinal axis.

While the illustrated embodiments use placement of the airflow port of each tank on one side of the channel recessed therein to enable the above described trapping of air on one side of the channel during removal of air therefrom to retain buoyancy of the tank at all times, other embodiments may employ other techniques for retaining a buoyancy of the lift at all times, for example by having an interior of each tank divided into a permanently sealed air containing portion and a separate portion connected to the air pump and having the water opening therein for selective filling and draining of that portion with air and water.

In other alternate embodiments, the means for pumping air into the tanks and releasing air therefrom may be separate, for example employing air fill ports fed by the air hoses from the air pump and openable and closeable air release ports for emptying air from the tank. The air control arrangement is also not limited to a single pump feeding all tanks, as multiple air pumps may be used, each feeding one or more of the tanks.

The illustrated embodiments feature three or four entirely separate tanks that are only interconnected by separate and distinct frame members. However, other embodiments, particularly those in which the frame is not adjustable in at least one of its length or width dimensions, may instead feature tank arrangements where two or more of the tanks are replaced with a single tank structure, either with independent interior air/water tanks spaces or compartments, or a shared hollow interior. For example, for pontoon boats, the two tanks on each side of the frame could be replaced with a respective single side-tank running the full length of a non-adjustable frame or a frame of adjustable width but non-adjustable length.

Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without department from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense. 

1. A boat lift for elevating a pontoon boat out of a body of water, the boat lift comprising: a frame having front and rear ends spaced along a longitudinal dimension and opposite first and second sides spaced apart in a transverse dimension perpendicular to the longitudinal dimension; a plurality of tanks mounted to the frame, including at least one first-side tank mounted to the frame adjacent the first side thereof and at least one second-side tank mounted to the frame adjacent the second side thereof, each tank comprising a shell enclosing a hollow interior, an air flow port that opens through the shell into the hollow interior, and a water port opening through the shell into the hollow interior adjacent a bottom of said hollow interior, wherein the shell of each tank has a concavely shaped upper end comprises two oppositely sloped walls positioned over the hollow interior of the shell and sloping upwardly and outwardly toward respective sides of the frame to define a channel that extends longitudinally of the frame between the sloped walls at a topside of the shell; an air pumping mechanism connected to the air flow port of each tank and operable to convey air into the hollow interior thereof to float the tanks into raised positions situating upper ends of the outwardly sloped walls above water level; and an air release mechanism connected to each tank and operable to release air from within the hollow interior thereof to decrease the buoyancy of the tanks for movement from the raised positions to lower positions, in which lower ends of the outwardly sloped walls and portions of the outwardly sloped walls that are found above water level in the raised positions are submerged below water level while the upper ends of the outwardly sloped walls remain above water level; wherein the channels of the first-side tank and the second-side tank are arranged to accommodate lower portions of first and second pontoons of the pontoon boat therein with the tanks in the lower positions for subsequent elevating of the pontoon boat out of the body of water by lifting of the pontoons by the upper ends of the tanks during movement of the tanks into the raised positions.
 2. (canceled)
 3. The boat lift of claim 1 wherein the at least one first-side tank comprises front and rear first-side tanks respectively disposed adjacent the front and rear ends of the frame, and the at least one second-side tank comprises front and rear second-side tanks respectively disposed adjacent the front and rear ends of the frame.
 4. (canceled)
 5. (canceled)
 6. (canceled)
 7. (canceled)
 8. (canceled)
 9. The boat lift of claim 1 wherein the air release mechanism comprises one or more valves each installed in an air passage that communicates with the hollow interiors of one or more of the tanks, each valve being operable to selectively open said air passage to release air from the hollow interior of the one or more tanks, and close said air passage, to retain air within the hollow interior of the one or more tanks.
 10. The boat lift of claim 9 wherein the air passage in which each valve is installed connects the air pump to the one or more tanks, and the air pumping mechanism is operable to convey air to said one or more tanks when said valve and said passage are open.
 11. The boat lift of claim 9 wherein the one or more valves comprises a plurality of valves, each operable to control air flow within the hollow interior of the shell of a respective one of the tanks.
 12. The boat lift of claim 11 comprising valve controls connected to the plurality of valves and operable for control thereof independently from one another.
 13. The boat lift of claim 1 comprising pump controls connected to the air pumping mechanism and operable for control over air-filling of each tank independently from one another.
 14. The boat lift of claim 1 wherein the frame comprises a width adjustment mechanism operable to change a width of the frame between the opposite first and second sides thereof.
 15. The boat lift of claim 1 wherein the frame comprises a length adjustment mechanism operable to change a length of the frame between the front and rear ends thereof.
 16. The boat lift of claim 14 wherein the width adjustment mechanism comprises at least one set of telescopically mated frame members, said frame members being slidable into, and lockable together in, different relative axial positions with one another to change an effective axial length spanned by said set.
 17. The boat lift of claim 1 comprising a stop device projecting upward to an elevation above the upper ends of the tanks adjacent the front end of the frame to limit movement of the boat over the frame from the rear end when the tanks are in the lowered positions.
 18. The boat lift of claim 17 wherein the stop device comprises at least one resilient bumper presenting an impact surface facing toward the rear end of the frame for contact therewith by the boat. 19-25. (canceled) 